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We have previously published data on cytogenetic anomalies in 657 employees of the Siberian Chemical Plant. The spectrum and frequency of cytogenetic anomalies in 1047 healthy workers of the Siberian Chemical Plant, depending on the age, gender, type of radiation, and external radiation dose, were studied in this study using a similar design. It was confirmed in a larger sample that the frequency of cytogenetic anomalies does not correlate with the gender of workers. There is a correlation between the age of workers and dicentric and ring chromosomes. Chronic external exposure to γ-radiation was the determining factor for the induction of cytogenetic anomalies. The frequency of cytogenetic anomalies in the blood of workers with combined irradiation was reduced in comparison with workers exposed only to external irradiation, which was caused by an additional radiation load due to the incorporated 239Pu. The dose dependence for aberrant cells, chromosomal aberrations, dicentric chromosomes, chromosomal (paired) and chromatid (unpaired) fragments, and chromatid exchanges had a nonlinear S-shaped character. Hormesis has been shown for aberrant cells, chromosomal aberrations, and chromosomal fragments, while it has not been confirmed for chromatid fragments. The threshold level of ionizing radiation for increasing the frequency of cytogenetic anomalies depended on their type and was realized in the range of 10–200 mGy. An expressed plateau was observed in the dose range of 100–800 mGy. The frequency of cytogenetic anomalies increased in direct proportion to the dose of external irradiation: after 500 mGy for dicentric chromosomes and after 800 mGy for other types. Dose dependence has not been found for ring chromosomes, abnormal monocentric chromosomes, multi-aberrant cells, and polyploid cells. [ABSTRACT FROM AUTHOR]